This invention relates generally to random access recording and playback apparatus and more particularly to apparatus for storing information on and/or retrieving information from a flexible, lightweight, grooveless recording disc.
The principles of the present invention are particularly useful in random access retrieval systems wherein a single item must be rapidly selected from a group of such items. For instance, reference may be made to U.S. Pat. No. 3,405,457, "Versatile Display Teaching System" issued to Donald L. Bitzer, wherein there is described a flexible computer controlled system for transmitting selected information to a number of student terminals. In such a computer-based education system, thousands of student terminals can be connected to a single computer. Each of these student terminals must be very flexible, providing random access audio information as well as video information in response to student inputs to the terminal, particularly where an audio response is better suited to the learning process than a visual response, e.g., in foreign language labs and the like.
In order to effectively aid the learning process in such applications, however, it is necessary that the substantial amounts of information be stored and that random access to the requested information be achieved with minimal delay. Many of the conventional storage apparatus, however, are not suitable to meet such requirements.
For example, in magnetic tape systems, the information is stored serially along the tape, and in order to access the desired information, it may be necessary to transport substantial lengths of the tape past the playback head before reaching that information. This not only results in slower response times but also produces tape wear as the tape is accessed to different storage locations, eventually degrading the quality of the audio played back.
Conventional recording disc turntables for playing back information stored on grooved discs are also undesirable. Because of the speed at which the disc must be rotated to access the information to be retrieved, the turntable platter develops a substantial angular momentum which is difficult to overcome when reducing the rotational speed to the level required for playback.
Another random access information retrieval apparatus adapted for use as a random access audio selector is disclosed in U.S. Pat. No. 3,738,227, issued to Donald L. Bitzer et al. In that apparatus, the audio selector was capable of randomly selecting any desired audio segment from 2,048 segments recorded along 64 radially spaced circular tracks of 32 segments each on a magnetic recording disc transported by a turntable during playback. Rapid access was provided by a novel spindle mechanism which lifted the disc from the turntable and rotated the disc at high speed to the desired audio segment. Specifically, the audio selector operated as a polar coordinate selection system having eleven 4-way control valves -- six for positioning a piston-cylinder train radially to any one of the 64 tracks and five for positioning another piston-cylinder train to rotate the disc angularly to any one of the 32 segments along each track.